1. Field of the Invention
The present invention relates to an endoscope apparatus for, for example, maintaining pipes used in plants and buildings; inspecting the inside of jet engines; and inspecting the inside of boilers. In particular, the present invention relates to an endoscope apparatus capable of being used in places potentially explosive.
2. Description of Related Art
An industrial endoscope apparatus is formed by a main unit and a scope unit attached to the main unit. An insertion portion formed by a flexible insertion tube is provided on the scope unit; and a CCD (charge-coupled-device) image pickup element is attached to a tip of this flexible insertion tube. In order to monitor the state of an object by using such an industrial endoscope apparatus the insertion portion is inserted into the object by the tip, and the state of the object is picked up by the CCD of the tip of the insertion portion. An image signal from the CCD element is transferred to the main unit; thus the picked up image of the object is displayed in on an LCD (Liquid Crystal Display) monitor on the main unit. Such industrial endoscope apparatuses have been commonly used for, for example, inspecting and researching various aspects in plants, and maintaining pipes.
If such industrial endoscope apparatus is used in an atmosphere containing combustible air or dust, it is preferable that the device be of explosion-protection structure. For such a purpose, as disclosed in Japanese Unexamined Patent Application, First Publication No. S57-211111, an explosion-protection structure has been proposed to prevent an explosion due to a short arc caused by the contact points of a plug when it is inserted into an electric outlet socket and a part of non-flammable air is introduced into an enclosure through an air-supplying pipe communicating with the inside of the enclosure and a contact point portion of the electrical outlet.
Here, explosion-protection specification is explained. The explosion-protection specification is standardized by, for example, IEC, ATEX (Europe), FM (U.S.A.), CSA (Canada), and TIIS (Japan): and these inspection organizations inspect explosion-protection apparatuses. In the present specification, the explosion-prevention specification is explained based on the IEC standard (IEC60079). Certainly, part of Japanese regulations may substantially coincide with those of other countries, and those standards may not be excluded in the explanation hereafter.
Considering the mechanism of explosion, explosions occur due to an ignition source increasing the temperature of an atmosphere containing combustible gas or dust, and oxygen. A fuel becomes a combustible gas or dust in, for example, gasoline tanks, factories, and engines, and in the air therearound. If there is an ignition source in such a state, an explosion may be induced. Conversely, factors for explosion are, firstly combustible gas or dust, secondly, oxygen, and thirdly an ignition source, i.e., an explosion will never occur if any one of them is lacking. Therefore, an endoscope system having an explosion-protection mechanism is achieved in the present invention by eliminating those factors induced by ignition sources.
IEC 60079 classifies locations where explosion-protection apparatuses are used as Zone 0, Zone 1, and Zone 2. Zone 0 indicates the most explosive location, Zone 1 indicates a less explosive location with respect to Zone 0, and Zone 2 indicates an ven less explosive location with respect to the Zone 1. These explosive zones are defined as hazardous areas, and areas having no explosion risk are defined as non-hazardous areas.
With respect to structure, explosion-protection apparatuses are defined as, an ia apparatus, an ib apparatus, and a Type-n apparatus. An “ia apparatus” indicates the most reliable explosion-protection, and an “ib apparatus” indicates the reliability is less than that of an ia apparatus. An ia apparatus can be used in Zone 0 and Zone 1. The ib apparatus can be used only in the Zone 1. Apparatuses that can be used in the Zone 0 and the Zone 1 are called intrinsically-safe-construction apparatuses. The Type-n apparatus can be used in the Zone 2.